Robo4 is a vascular-specific receptor that inhibits endothelial migration

Abstract

Guidance and patterning of axons are orchestrated by cell-surface receptors and ligands that provide directional cues. Interactions between the Robo receptor and Slit ligand families of proteins initiate signaling cascades that repel axonal outgrowth. Although the vascular and nervous systems grow as parallel networks, the mechanisms by which the vascular endothelial cells are guided to their appropriate positions remain obscure. We have identified a putative Robo homologue, Robo4, based on its differential expression in mutant mice with defects in vascular sprouting. In contrast to known neuronal Robo family members, the arrangement of the extracellular domains of Robo4 diverges significantly from that of all other Robo family members. Moreover, Robo4 is specifically expressed in the vascular endothelium during murine embryonic development. We show that Robo4 binds Slit and inhibits cellular migration in a heterologous expression system, analogous to the role of known Robo receptors in the nervous system. Immunoprecipitation studies indicate that Robo4 binds to Mena, a known effector of Robo-Slit signaling. Finally, we show that Robo4 is the only Robo family member expressed in primary endothelial cells and that application of Slit inhibits their migration. These data demonstrate that Robo4 is a bona fide member of the Robo family and may provide a repulsive cue to migrating endothelial cells during vascular development.

Slit modulates cerebrovascular inflammation and mediates neuroprotection against global cerebral ischemia

“…The interaction between srGAPs and Rho GTPases changes the relative balance between the active and inactive Rho GTPase forms, and abolishes the directional mobility of the cell towards chemoattractants (Wong et al, 2001). In addition to the leukocyte-based mechanism outlined above, Slit might exert its anti-chemotactic effect by negative regulation of Rho GTPase signaling in endothelial cells, which also express Slit receptors (Park et al, 2003;Wang et al, 2003). The inhibition of Rho-mediated cascades by Slit engagement of these receptors could lead to increased expression and activity of endothelial nitric oxide synthase (Laufs et al, 2000), a potent antiinflammatory mediator (Altay et al, 2004;Kubes et al, 1991), and decreased ICAM-1-mediated signaling (Adamson et al, 1999) within the endothelial cell.…”

The brain within the tumor: new roles for axon guidance molecules in cancers

“…105 However, it lacks some of the Ig domains and FNIII domains found in other robo proteins and its capacity to bind slits is still debated. 106,107 The N terminal region of slits contains a stretch of four leucine-rich repeat domains (LRR) connected by disulfide bonds. These and the Ig domains of robo are important for signaling.…”

Potential role of the Slit/Robo signal pathway in angiogenesis

“…22 Utilizing differential display technique (wild type vs Alk1 Ϫ/Ϫ mice), they found a fivefold increase of Robo4 mRNA expression. 20 In the normal mice, Robo4 mRNA expression was determined by in situ hybridization, and at E9.0, Robo4 mRNA was positively expressed in the dorsal aorta and intersomitic vessels. Soon, in the dorsal aorta, its expression gradually disappeared, and by E10.0, Robo4 mRNA expression expanded to smaller vessels.…”

“…Soon, in the dorsal aorta, its expression gradually disappeared, and by E10.0, Robo4 mRNA expression expanded to smaller vessels. 20 To further investigate the expression pattern of Robo4, both Northern blot analysis and immunohistochemical staining were performed in adult tissues. Robo4 mRNA was highly expressed in the heart, moderately in the liver, kidney, and lung, and was undetectable in the brain, skeletal muscle, spleen, and testis as determined by Northern blot analysis.…”